1. Field of the Invention
The present invention relates to a hull form of a vessel, and more particularly to a position where a propeller shaft is installed.
2. Description of the Related Art
A body plan of a single-screw hull equipped with a conventional symmetric type stern is shown in FIG. 1, wherein reference numeral 1 denotes a transverse sectional shape, 2 denotes the hull center line, 3 denotes a propeller shaft, 4 denotes a propeller disc plane and WL denotes a load waterline. It is well known that the propeller shaft is usually provided on the vertical central plane of the hull, for a conventional type of a single-screw vessel.
When the propeller shaft is installed in such a position, water inflows to the propeller disc plane are shown in FIGS. 2(A) and 2(B). FIGS. 2(A) and 2(B) represent graphically water inflow speed to the propeller disc plane. FIG. 2(A) is a representation of wake distribution, and FIG. 2(B) is a vector diagram for transverse velocity of water. Curved line (a) shows a ratio of wake speed generated on the propeller disc plane in relation to vessel speed, and vector (b) shows the transverse direction of wake velocity generated on every point of the propeller disc plane. As clearly understood from these representations, inflows to the propeller disc plane are formed into symmetrical flows with regard to propeller shaft 3. In this manner, complicated distribution of wakes are generated while the vessel is sailing. As shown in FIG. 3, the wakes become symmetrical with regard to propeller shaft 3 positioned on the vertical center plane 2 of the hull.
Vessels with high block coefficient and wide breadth have been increasing in number to raise loading capacity. Owing to this high blockage coefficient and wide breadth, vertical vortices around longitudinal axes are generated on the propeller disc plane, from the aforementioned wakes. These vertical vortices are generated in pairs by both sides of a vessel, unbalancing the wakes on the propeller disc plane. This results in reducing efficiency in propulsion and increasing hull-resistance. In those circumstances, there has been demanded a reduction of the ratio of fuel consumption for sailing as well as improvement in loading capacity. To satisfy this demand, improvement in propulsive efficiency is indispensable.